I have added some more error handling to the validation process of the skin admin page.
This is something I have had around for a bit, but finally enabled. It does specific file size checks on the bitmaps being submitted. The file is not the exact size it should be, an error will be thrown.
I need to hear from anyone who is getting that error, if they are sure the image files are the correct format and pixel size.
Some editors may add extraneous bytes to the end of the file for their own use. Photoshop does not, but I am not sure about Gimp, or others.